Spatially-doped charge transport layers

ABSTRACT

The present invention relates to new a charge transport layer that includes first charge transport material which is spatially doped with a second charge transport material. The charge transport layer may either be a hole or electron transport layer and is useful in organic electronic devices.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to charge transport layers useful inorganic electronic devices. The invention further relates to electronicdevices in which there is at least one such charge transport layer.

2. Background

In organic electronic devices, such as organic light-emitting diodes(“OLEDs”), that make up displays, the organic active layer is sandwichedbetween two electrical contact layers. In an OLED the organic activelayer is photoactive where upon application of a voltage across theelectrical contact layers, the contact layers generatepositively-charged holes and negatively charged electrons, which combinein the photoactive layer and cause photon generation. At least one ofthe electrical contact layers is transparent or translucent so that thegenerated photons can pass through the electrical contact layer andescape the device.

It is well known to use organic electroluminescent compounds as thephotoactive component in OLEDs. Simple organic molecules, conjugatedpolymers, and organometallic complexes have been used.

These devices frequently include one or more charge transport layers,which are positioned between the photoactive (e.g., light-emitting)layer and one or both of the contact layers. A hole transport layer maybe positioned between the photoactive layer and the hole-injectingcontact layer, also called the anode. An electron transport layer may bepositioned between the photoactive layer and the electron-injectingcontact layer, also called the cathode.

There is a continuing need for charge transport layers.

SUMMARY OF THE INVENTION

A new charge transport layer is provided comprising a host chargetransport material and a guest charge transport material, wherein saidguest material is spatially doped within the host material.

The foregoing general description and the following detailed descriptionare exemplary and explanatory only and are not restrictive of theinvention, as defined in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is illustrated by way of example and not limitation in theaccompanying figures.

FIG. 1: A schematic diagram of a prior art OLED device.

FIG. 2: A schematic diagram of another prior art OLED device.

FIG. 3: A schematic diagram of an OLED device having one embodiment ofthe new charge transport layer.

FIG. 4: A schematic diagram of an OLED device having another embodimentof the new charge transport layer

FIG. 5: A comparison of radiance vs voltage curves for OLED devices madewith one embodiment of the new charge transport layer (a hole transportlayer) (curve 5-a) and with conventional hole transport layers (curves5-b and 5-c).

FIG. 6: A comparison of efficiency vs voltage curves for OLED devicesmade with one embodiment of the new charge transport layer (a holetransport layer) (curve 6-a) and with conventional hole transport layers(curves 6-b and 6-c).

FIGS. 7-10: Are schematic diagrams of an OLED device having otherembodiments of a new charge transport layer.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A new charge transport layer comprises a host charge transport materialand a guest charge transport material, wherein said guest material isspatially doped within the host material.

Another embodiment is a new organic electronic device having at leastone charge transport layer comprising a host charge transport materialand a guest charge transport material, wherein said guest material isspatially doped within the host material.

As used herein, the term “charge transport material” is intended to meana compound or combination of compounds that can receive a charge from anelectrode and facilitate its movement through the thickness of thematerial with relatively high efficiency and small loss of charge. Holetransport materials are capable of receiving a positive charge from ananode and transporting it. Electron transport materials are capable ofreceiving a negative charge from a cathode and transporting it.

As used herein, the term “host” is intended to mean a material which ispresent in an amount equal to or greater than 50% by weight of thecharge transport layer. The term “guest” is intended to mean a materialwhich is present in an amount equal to or less than 50% by weight of thecharge transport layer. In one embodiment, the host is at least 60% ofthe charge transport layer. In one embodiment, the host is at least 75%of the charge transport layer. In one embodiment, the host is at least85% by weight of the charge transport layer. In another embodiment, thehost is at least 90% by weight of the charge transport layer. In anotherembodiment, the host is at least 95% by weight of the charge transportlayer.

As used herein, the term “spatially doped” is intended to mean that afirst material (guest) is located in a spatially discrete areas within asecond material (host) such that together the two materials create acharge transport layer (e.g., the first material is neither distributedin the second material so as to create a substantially uniform orhomogenous composition of the two materials nor are the two materialsused to create separate layers of two of the materials in the device.)Rather the guest is located within the host in spatially discretelocations as shown, for example in FIGS. 3, 4, and 7-10.

Moreover, the first and second materials may be compositions comprisingtwo or more charge transport components (such as two or more compoundsand/or polymers), or may be compositions comprising one or morecomponents that provide substantially all of the charge transportcharacteristics of the material and one or more component that provideslittle or no charge transport characteristics of the material.

In selecting guest and host materials for use in the new chargetransport layer, the guest and host materials should be sufficientlycompatible with one another so as to not significantly trap either holesor electrons (depending on whether such is a hole transport layer or anelectron transport layer, respectively). Any number of techniques can beused to determine presence and degree of charge traps and suchtechniques include (1) impedance spectroscopy and (2) thermallystimulated currents.

Moreover, the new charge transport layer should be sufficientlycompatible with the layers of the organic electronic device in which itis used so as to not significantly trap either holes or electrons(depending on whether such is a hole transport layer or an electrontransport layer, respectively), which can also be determined asexplained above. In one embodiment, both the host and guest materialsare hole transport materials. Examples of hole transport materials havebeen summarized in, for example, Kirk-Othmer Encyclopedia of ChemicalTechnology, Fourth Edition, Vol. 18, p. 837-860, 1996, by Y. Wang. Bothhole transporting molecules and polymers can be used. Commonly used holetransporting molecules include, but are not limited to:N,N′-diphenyl-N,N′-bis(3-methylphenyl)-[1,1′-biphenyl]-4,4′-diamine(TPD), 1,1-bis[(di4-tolylamino) phenyl]cyclohexane (TAPC),N,N′-bis(4-methylphenyl)-N,N′-bis(4-ethylphenyl)-[1,1′-(3,3′-dimethyl)biphenyl]-4,4′-diamine(ETPD), tetrakis-(3-methylphenyl)-N,N,N′, N′-2,5-phenylenediamine (PDA),a-phenyl-4-N,N-diphenylaminostyrene (TPS), p-(diethylamino)benzaldehydediphenylhydrazone (DEH), triphenylamine (TPA),bis[4-(N,N-diethylamino)-2-methylphenyl](4-methylphenyl)methane (MPMP),1-phenyl-3-[p-(diethylamino)styryl]-5-[p-(diethylamino)phenyl]pyrazoline (PPR or DEASP), 1,2-trans-bis(9H-carbazol-9-yl)cyclobutane(DCZB), N,N,N′, N′-tetrakis(4-methylphenyl)-(1,1′-biphenyl)4,4′-diamine(TTB), 4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (NPB or NPD),carbazole biphenyl (CBP), and porphyrinic compounds, such as copperphthalocyanine. Commonly used hole transporting polymers include, butare not limited to polyvinylcarbazole, (phenylmethyl)polysilane,polythiophenes, such as poly(3,4-ethylenedioxythiophene), polypyrroles,and polyanilines. It is also possible to obtain hole transportingmaterials by doping hole transporting molecules such as those mentionedabove into polymers, including those that are not typically chargetransporting such as polystyrene and polycarbonate. In such a dopedpolymer, the hole transporting molecules are distributed throughout thepolymer in a fashion to achieve a substantially homogenous composition(to the extent possible in view of the specific polymer(s) and holetransport molecule(s) selected). In one embodiment of the new chargetransport layer, a polymer substantially-homogenously doped with holetransporting molecules is used as one of the charge transport materials(either in the host or guest material).

In one embodiment, the host hole transport material used in new chargetransport layer is selected from any of the hole transport materialsgiven above or mixtures thereof. In one embodiment, the host has a highmobility for holes (positive charges), >10⁻⁶ cm²N/sec at the operatingvoltage. Its highest occupied molecular orbital (“HOMO”) levels shouldbe selected to allow low barrier hole injection from the anode. In oneembodiment, the host is also capable of transporting electrons, with amobility >10⁻⁷ cm²N/sec at the operating voltage. The thickness of thehost hole transport layer can range between 1 nm to 1000 nm. In oneembodiment, the host thickness is from 10 nm to 500 nm.

In one embodiment, the guest hole transport material is selected fromany of the above hole transport materials or mixtures thereof, but isdifferent from the host material. In one embodiment, the guest materialhas a high mobility for holes (positive charges), >10⁻⁶ cm²N/sec at theoperating voltage. In one embodiment, the lowest unoccupied molecularorbital (“LUMO”) level of the guest hole transport material is higherthan the LUMO level of the host hole transport material. “Higher” isdefined as closer to the vacuum level which is energy zero, so “higherenergy” means the absolute value of the energy is smaller.

In one embodiment, the new charge transport layer comprises a host holetransport material that comprises a compound having at least twocarbazole groups and the guest hole transport material comprises atriarylmethane compound.

In one embodiment, the new charge transport layer comprises host holetransport material that comprises a compound of Formula I below:

wherein E is selected from a single bond, (CR¹R²)_(m), O, S,(SiR¹R²)_(m) wherein m is an integer of 1 to 20, wherein R¹ and R² areeach independently selected from H, F, alkyl, aryl, alkoxy, aryloxy,fluoroalkyl, fluoroaryl, fluoroalkoxy, and fluoroaryloxy, and wherein R¹and R² can, when taken together, can form 5- or 6-membered rings.

In one embodiment, the new charge transport comprises a guest holetransport material that comprises a compound of Formula II below:

wherein:

Ar¹ can be the same or different at each occurrence and is selected fromaryl and heteroaryl;

R³ can be the same or different at each occurrence and is selected fromH, alkyl, heteroalkyl, aryl, heteroaryl, arylalkylene,heteroarylalkylene, C_(n)H_(a)F_(b), and C₆H_(c)F_(d); or adjacent R³groups can be joined to form 5- or 6-membered rings;

X can be the same or different at each occurrence and is selected fromR³, alkenyl, alkynyl, N(R¹)₂, OR¹, OC_(n)H_(a)F_(b), OC₆H_(c)F_(d),halide, NO₂, OH, CN, and COOR¹;

n is an integer, and

a, b, c, and d are 0 or an integer such that a+b =2n+1, and c+d =5.

In one embodiment, the host is CBP and the guest is MPMP.

In one embodiment, both the host and guest charge transport materialsare electron transport materials. Examples of electron transportmaterials include, but are not limited to, metal chelated oxinoidcompounds, such asbis(2-methyl-8-quinolinolato)(para-phenyl-phenolato)aluminum(III) (BAIQ)and tris(8-hydroxyquinolato)aluminum (Alq₃); azole compounds such as2-(4-biphenylyl)-5-(4-t-butylphenyl)-1,3,4-oxadiazole (PBD),3-(4-biphenylyl)-4-phenyl-5-(4-t-butylphenyl)-1,2,4-triazole (TAZ), and1,3,5-tri(phenyl-2-benzimidazole)benzene (TPBI); quinoxaline derivativessuch as 2,3-bis(4-fluorophenyl)quinoxaline; phenanthroline derivativessuch as 9,10-diphenylphenanthroline (DPA) and2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (DDPA); and mixturesthereof.

In one embodiment, the host electron transport material used in the newcharge transport layer is selected from any of the electron transportmaterials given above or mixtures thereof. In one embodiment, the hosthas a high mobility for electrons, >10⁻⁸ cm²N/sec at the operatingvoltage. Its lowest un-occupied molecular orbital (“LUMO”) levels shouldbe selected to allow low barrier electron injection from the cathode.The thickness of the host electron transport layer can range between 1nm to 1000 nm. In one embodiment, the host thickness is from 10 nm to500 nm.

In one embodiment, the guest electron transport material is selectedfrom any of the above electron transport materials, but is differentfrom the host material. In one embodiment, the guest material has a highmobility for electrons, >10⁻⁸ cm²N/sec at the operating voltage. In oneembodiment, the highest occupied molecular orbital (“HOMO”) level of theguest electron transport material is lower than the HOMO level of thehost electron transport material. “Lower” is defined as further awayfrom the vacuum level which is energy zero, so “lower energy” means theabsolute value of the energy is larger.

Spatial doping of the guest charge transport material in the hostmaterial can combine the positive attributes of different chargetransport materials.

Embodiments of the new charge transport layer include the discretelayers of the guest materials at any desired location within the hostmaterial. For example, in one embodiment, the new charge transport layercomprises the guest charge transport material spatially doped as a thinsublayer within the host material.

In another embodiment, the guest material is discretely deposited andlocated at the approximate center of the host material in the new chargetransport layer, or it can be discretely positioned toward the top orbottom of the host material. In one embodiment, the guest materialcreates a sublayer having a thickness within the host material that isless than 50% of the thickness of the host material used in the newcharge transport layer. In one embodiment, the thickness of the guestsublayer is from 1% to 20% of the thickness of the host material asdeposited. In one embodiment, it is from 2% to 10% of the thickness ofthe host material as deposited. In one embodiment, the guest sublayer isless than 5 nm in thickness. In one embodiment, the guest sublayer isless than 2 nm.

In other embodiments, the guest charge transport material can bedeposited so as to have different configurations within the host chargetransport material. In one embodiment, the guest material is present asmore than one sub layer within the host material in the new chargetransport layer. In one embodiment, the guest material is present as alayer having discontinuities. In one embodiment, the guest material ispresent as multiple discrete islands within the host material. Theislands may be the same size or different sizes. In one embodiment, theguest material is present at differing amounts or gradations, the guestconcentration varying across the thickness of the host material. That isthe multiple discrete islands may have differing thicknesses and/or belocated at differing discrete locations so that some are closer to theelectrode side of the charge transport layer, while other discreteislands are in the approximate center of the charge transport layer,while still others are nearer to the other active layers in the organicelectronic device.

Electronic Device

Another embodiment is a new organic electronic device having at leastone charge transport layer comprising a host charge transport materialand a guest charge transport material, wherein said guest material isspatially doped within the host material.

Organic electronic devices that may benefit from having one or more thenew charge transport layer include, but are not limited to, (1) devicesthat convert electrical energy into radiation (e.g., a light-emittingdiode, light emitting diode display, or diode laser), (2) devices thatdetect signals through electronics processes (e.g., photodetectors.,photoconductive cells, photoresistors, photoswitches, phototransistors,phototubes, IR detectors), (3) devices that convert radiation intoelectrical energy, (e.g., a photovoltaic device or solar cell), and (4)devices that include one or more electronic components that include oneor more organic semi-conductor layers (e.g., a transistor or diode).Other uses for the new charge transport layers include photoconductorsand electrophotographic devices.

In one embodiment, the new organic electronic device is an OLED. Ingeneral, this device comprises a photoactive layer positioned betweentwo electrical contact layers. Specific embodiments of the new chargetransport layer of the present invention may be used between thephotoactive layer and the first contact layer (anode) as a holetransport layer and/or between the photoactive layer and the secondcontact layer (cathode) as an electron transport layer The device mayinclude a support or substrate, onto which the active materials aredeposited, that can be adjacent to the anode layer or the cathode layer.

The anode is an electrode that is particularly efficient for injectingpositive charge carriers. It can be made of, for example materialscontaining a metal, mixed metal, alloy, metal oxide or mixed-metaloxide, or it can be a conducting polymer, and mixtures thereof. Suitablemetals include the Group 11 metals, the metals in Groups 4, 5, and 6,and the Group 8-10 transition metals. If the anode is to belight-transmitting, mixed-metal oxides of Groups 12, 13 and 14 metals,such as indium-tin-oxide (“ITO”), are generally used. The anode may alsocomprise an organic material such as polyaniline as described in“Flexible light-emitting diodes made from soluble conducting polymer,”Nature vol. 357, pp 477-479 (11 Jun. 1992). The cathode is an electrodethat is particularly efficient for injecting electrons or negativecharge carriers. The cathode can be any metal or nonmetal having a lowerwork function than the anode. Materials for the cathode can be selectedfrom alkali metals of Group 1 (e.g., Li, Cs), the Group 2 (alkalineearth) metals, the Group 12 metals, including the rare earth elementsand lanthanides, and the actinides and mixtures thereof. Materials suchas aluminum, indium, calcium, barium, samarium and magnesium, as well ascombinations, can be used. Li-containing organometallic compounds, LiF,and Li₂O can also be deposited between the organic layer and the cathodelayer to lower the operating voltage. Examples include LiF/Al and Mg/Ag.

With respect to OLED devices, at least one of the anode and cathodeshould be at least partially transparent to allow the generated light tobe observed.

In an OLED device, the photoactive layer may typically comprise anyorganic electroluminescent (“EL”) material, including, but not limitedto, fluorescent dyes, fluorescent and phosphorescent metal complexes,conjugated polymers, and mixtures thereof. Examples of fluorescent dyesinclude, but are not limited to, pyrene, perylene, rubrene, derivativesthereof, and mixtures thereof. Examples of metal complexes include, butare not limited to, metal chelated oxinoid compounds, such astris(8-hydroxyquinolato)aluminum (Alq3); and cyclometalated iridium andplatinum electroluminescent compounds. Examples of conjugated polymersinclude, but are not limited to poly(phenylenevinylenes), polyfluorenes,poly(spirobifluorenes), polythiophenes, poly(p-phenylenes), copolymersthereof, and mixtures thereof.

In one embodiment, the photoactive material is an organometallicelectroluminescent compound. In one embodiment, the photoactive materialis selected from cyclometalated iridium and platinum electroluminescentcompounds and mixtures thereof. Complexes of Iridium withphenylpyridine, phenylquinoline, or phenylpyrimidine ligands have beendisclosed as electroluminescent compounds in Petrov et al., PublishedPCT Application WO 02/02714. Other organometallic complexes have beendescribed in, for example, published applications US 2001/0019782, EP1191612, WO 02/15645, and EP 1191614. Electroluminescent devices with anactive layer of polyvinyl carbazole (PVK) doped with metallic complexesof iridium have been described by Burrows and Thompson in published PCTapplications WO 00/70655 and WO 01/41512. Electroluminescent emissivelayers comprising a charge carrying host material and a phosphorescentplatinum complex have been described by Thompson et al., in U.S. Pat.No. 6,303,238, Bradley et al., in Synth. Met. (2001), 116 (1-3),379-383, and Campbell et al., in Phys. Rev. B, Vol. 65 085210. Analogoustetradentate platinum complexes can also be used. Theseelectroluminescent complexes can be used alone, or doped intocharge-carrying hosts, as noted above.

In one embodiment, the new charge transport layer is a spatially-dopedhole transport layer and the electron transport layer comprises anyconventional electron transport material, as described above. This isillustrated in FIG. 3. Layer 310 is a substantially transparent anode,typically ITO. Optional layer 315 is a hole injection layer. Aspatially-doped hole transport layer 320 is on top of the hole injectionlayer, when present, or the cathode. The spatially-doped hole transportlayer comprises a host hole transport Imaterial 321, spatially dopedwith an ultra thin guest hole transport sub layer 325.

FIGS. 7 -10 illustrate other exemplary embodiments of discretely locatedguest hole transport materials within the host hole transport material.In the illustrated example of FIGS. 3, and 7-10, a photoactive layer 330is on top of the spatially doped hole transport layer, 320. In thisillustration, the photoactive layer is luminescent. An electrontransport layer 340 is on top of the photoactive layer. Optionally, anelectron injection layer 350 is on top of the electron transport layer.An electron injection layer, as used herein, is a layer that receiveselectrons from the cathode and transports them to the electron transportlayer and/or another active layer, such as light emitting layer in anOLED. A cathode 360 is on top of the electron injection layer, whenpresent, or the photoactive layer.

In one embodiment, the new charge transport layer is an electrontransport layer is a spatially-doped electron transport layer and thehole transport layer comprises any conventional hole transport material,as described above. This is illustrated in FIG. 4, which is a example ofone OLED device. Layer 410 is a substantially transparent anode,typically ITO. Optional layer 415 is a hole injection layer. A holetransport layer 420 is on top of the hole injection layer, when present,or the anode. A photoactive layer 430 is on top of the hole transportlayer. In this illustration, the photoactive layer is luminescent. Aspatially-doped electron transport layer 440 is on top of thephotoactive layer. The spatially-doped layer comprises a host electrontransport material 441, spatially doped with an ultra thin guestelectron transport material as sublayer 445. It should be appreciatedthat the illustrations of the discrete locations of the guest materialin the host material illustrated in FIGS. 7 through 10 are equallyapplicable for an electron transport layer, but specific figures are notshown. Optionally, an electron injection layer 450 is on top of theelectron transport layer. An electron injection layer, as used herein,is a layer that receives electrons from the cathode and transports themto the electron transport layer and/or light emitting layer. A cathode460 is on top of the electron injection layer, when present, or thephotoactive layer. Typically, the cathode is LiF/Al or Mg/Ag.

In one embodiment, an organic device comprises at least one holetransport layer that is one embodiment of the new charge transport layerof the present invention and at least one electron transport layer thatis another embodiment of the new charge transport layer of the presentinvention.

It is known to have other layers in organic electronic devices. Forexample, there can be a layer between the anode and the hole transportlayer to facilitate positive charge transport and/or band-gap matchingof the layers, or to function as a protective layer. Layers that areknown in the art can be used. In addition, any of the above-describedlayers can be made of two or more layers. Alternatively, some or all ofthe anode layer, the hole transport layer, the electron transportlayers, and the cathode layer, may be surface treated to increase chargecarrier transport efficiency. The choice of materials for each of thecomponent layers is preferably determined by balancing the goals ofproviding a device with high device efficiency with device operationallifetime.

It is understood that each functional layer may be made up of more thanone layer.

The device can be prepared by depositing the various materials using anyknown technique, including, but not limited to vapor depositiontechniques, liquid deposition techniques, thermal transfer techniques,and combinations thereof. The individual layers are sequentiallydeposited on a suitable substrate. Substrates such as glass, ceramic,metals, and polymeric films can be used. Conventional vapor depositiontechniques can be used, such as thermal evaporation, chemical vapordeposition, and the like. Alternatively, the organic layers can beapplied using liquid deposition techniques. The liquid can be in theform of a solution, dispersion, suspension, emulsion, or the like.Typical liquid deposition techniques include, but are not limited to,continuous deposition techniques such as spin coating, gravure coating,curtain coating, dip coating, slot-die coating, spray coating, andcontinuous nozzle coating; and discontinuous deposition techniques suchas ink jet printing, gravure printing, and screen printing. To achievethe new charge transport layer of the present invention, the guestmaterial and host material are deposited discretely and may be depositedusing the same or different techniques, depending on the actualmaterials and other fabrication considerations for a particular device.

In general, the different layers will have the following range ofthicknesses: anode 110, 500-5000 Å, in one embodiment 1000-2000 Å; holetransport layer 120, 50-2000 Å, in one embodiment 200-1000 Å;photoactive layer 130, 10-2000 Å, in one embodiment 100-1000 Å; electrontransport layer 140 and 150, 50-2000 Å, in one embodiment 100-1000 Å;cathode 160, 200-10000 Å, in one embodiment 300-5000 Å. The location ofthe electron-hole recombination zone in the device, and thus theemission spectrum of the device, can be affected by the relativethickness of each layer. For example, with respect to an OLED, thethickness of the electron-transport layer should be chosen so that theelectron-hole recombination zone is in the light-emitting layer. Thedesired ratio of layer thicknesses will depend on the exact nature ofthe materials used.

As used herein, the term “alkyl” is intended to mean a group derivedfrom an aliphatic hydrocarbon having one point of attachment. The term“alkenyl” is intended to mean a group derived from a hydrocarbon havingone or more carbon-carbon double bonds and having one point ofattachment. The term “alkynyl” is intended to mean a group derived froma hydrocarbon having one or more carbon-carbon triple bonds and havingone point of attachment. The term “aryl” is intended to mean a groupderived from an aromatic hydrocarbon having one point of attachment. Theterm “arylalkylene” is intended to mean a group derived from an alkylgroup having an aryl substituent. The term “alkoxy” refers to an alkylgroup attached to an oxygen atom, and further attached to anothermolecule by the oxygen. The term “aryloxy” refers to an aryl groupattached to an oxygen atom, and further attached to another molecule bythe oxygen.

The term “group” is intended to mean a part of a compound, such as asubstituent in an organic compound.

The term “compound” is intended to mean an electrically unchargedsubstance made up of molecules that further consist of atoms, whereinthe atoms cannot be separated by physical means.

The term “layer” is used interchangeably with the term “film” and refersto a coating covering a desired area. The area can be as large as anentire device or a specific functional area such as the actual visualdisplay, or as small as a single sub-pixel. Films can be formed by anyconventional deposition technique, including vapor deposition and liquiddeposition.

As used herein, the terms “emitter”, “luminescent material”, or“photoactive” refer to a material that emits light when activated by anapplied voltage (such as in a light-emitting diode or light-emittingelectrochemical cell), or responds to radiant energy and generates asignal with or without an applied bias voltage (such as in aphotodetector or photoconductor), as the case may be in the specificdevice, as will be understood from the context.

As used herein, an “organometallic compound” is a compound having ametal-carbon bond. The organometallic compound may include metal atomsfrom Groups 3 through 15 of the Periodic Table and mixtures thereof.

The prefix “hetero” indicates that one or more carbon atoms has beenreplaced with a different atom.

The prefix “fluoro” indicates that one or more hydrogens bonded to acarbon has been replaced with fluorine.

Unless otherwise indicated, all groups can be unsubstituted orsubstituted. Unless otherwise indicated, all groups can be linear,branched or cyclic, where possible. Unless otherwise indicated, allgroups can have from 1-30 carbon atoms.

The phrase “adjacent to,” when used to refer to layers in a device, doesnot necessarily mean that one layer is immediately next to anotherlayer. On the other hand, the phrase “adjacent R groups” is used torefer to R groups that are next to each other in a chemical formula(i.e., R groups that are on atoms joined by a bond).

The IUPAC number system is used throughout, where the groups from thePeriodic Table are numbered from left to right as 1-18 (CRC Handbook ofChemistry and Physics, 81^(st) Edition, 2000).

As used herein, the phrase “X is selected from A, B, and C” isequivalent to the phrase “X is selected from the group consisting of A,B, and C”, and is intended to mean that X is A, or X is B, or X is C.The phrase “X is selected from 1 through n” is intended to mean that Xis 1, or X is 2, . . . or X is n.

As used herein, the terms “comprises,” “comprising,” “includes,”“including,” “has,” “having” or any other variation thereof, areintended to cover a non-exclusive inclusion. For example, a process,method, article, or apparatus that comprises a list of elements is notnecessarily limited to only those elements but may include otherelements not expressly listed or inherent to such process, method,article, or apparatus. Further, unless expressly stated to the contrary,“or” refers to an inclusive or and not to an exclusive or. For example,a condition A or B is satisfied by any one of the following: A is true(or present) and B is false (or not present), A is false (or notpresent) and B is true (or present), and both A and B are true (orpresent).

Also, use of the “a” or “an” are employed to describe elements andcomponents of the invention. This is done merely for convenience and togive a general sense of the invention. This description should be readto include one or at least one and the singular also includes the pluralunless it is obvious that it is meant otherwise.

Unless otherwise defined, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this invention belongs. Unless otherwise defined, allletter symbols in the figures represent atoms with that atomicabbreviation. Although methods and materials similar or equivalent tothose described herein can be used in the practice or testing of thepresent invention, suitable methods and materials are described below.All publications, patent applications, patents, and other referencesmentioned herein are incorporated by reference in their entirety. Incase of conflict, the present specification, including definitions, willcontrol. In addition, the materials, methods, and examples areillustrative only and not intended to be limiting.

The new charge transport layer and its uses will now be described byreference to the following non-limiting examples.

EXAMPLES

The following examples illustrate certain features and advantages of thepresent invention. They are intended to be illustrative of theinvention, but not limiting. All percentages are by weight, unlessotherwise indicated.

General Procedure

OLED devices were fabricated by the thermal evaporation technique. Thebase vacuum for all of the thin film deposition was in the range of 10⁻⁶torr. The deposition chamber was capable of depositing eight differentfilms without the need to break the vacuum. Patterned indium tin oxidecoated glass substrates from Thin Film Devices, Inc were used. TheseITO's are based on Corning 1737 glass coated with 1400 Å ITO coating,with sheet resistance of 30 ohms/square and 80% light transmission. Thepatterned ITO substrates were then cleaned ultrasonically in aqueousdetergent solution. The substrates were then rinsed with distilledwater, followed by isopropanol, and then degreased in toluene vapor.

The cleaned, patterned ITO substrate was then loaded into the vacuumchamber and the chamber was pumped down to 10⁻⁶ torr. The substrate wasthen further cleaned using an oxygen plasma for about 5 minutes. Aftercleaning, multiple layers of thin films were then deposited sequentiallyonto the substrate by thermal evaporation. Patterned metal electrodes(Al or LiF/Al) were deposited through a mask. The thickness of the filmwas measured during deposition using a quartz crystal monitor. Thecompleted OLED device was then taken out of the vacuum chamber andcharacterized immediately without encapsulation.

The OLED samples were characterized by measuring their (1)current-voltage (I-V) curves, (2) electroluminescence radiance versusvoltage, and (3) electroluminescence spectra versus voltage. The I-Vcurves were measured with a Keithley Source-Measurement Unit Model 237.The electroluminescence radiance (in the unit of cd/m²) vs. voltage wasmeasured with a Minolta LS-110 luminescence meter, while the voltage wasscanned using the Keithley SMU. The electroluminescence spectrum wasobtained by collecting light using an optical fiber, through anelectronic shutter, dispersed through a spectrograph, and then measuredwith a diode array detector. All three measurements were performed atthe same time and controlled by a computer. The efficiency of the deviceat a certain voltage is determined by dividing the electroluminescenceradiance of the LED by the current density needed to run the device. Theunit is in cd/A.

Materials used in the examples are listed below. MPMP is the guest holetransport material, CBP is the host hole transport material, DPA is theelectron transport material, AIQ is the electron injection material, andG1 is a green emitter. Their molecular structures are shown in thefollowing:

Comparative Example 1

In this comparative example a device was made having a prior artstructure, as shown in FIG. 1. The device 100 has an anode layer 110 anda cathode layer 160. Adjacent to the anode is a layer 120 comprisinghole transport material. Adjacent to the cathode is a layer 140comprising two electron transport material Between the hole transportlayer and the electron transport layer is the photoactive layer 130. Asan option, devices frequently use another electron injection layer 150,next to the cathode, and/or another hole injection layer 115, next tothe anode. In this example, optional layer 115 is not present.

The device was made according to the General Procedure with thefollowing configuration, with layer thicknesses given in parenthesis:

Substrate: glass

Anode: ITO

Hole transport layer: MPMP (304 Å)

Emitter: G1 (401 Å)

Electron transport layer: DPA (102 Å)

Electron transport layer: AlQ(303 Å)

Cathode: LiF(10 Å)/Al(505 Å)

The device emits green light with an electroluminescent efficiency of 25cd/A at 13 V, and a radiance of 10,000 cd/m2 at 19 V. Its radiance vs.voltage curve is shown in FIG. 5, as 5-c. Its efficiency vs. voltagecurve is shown in FIG. 6, as 6-c.

Comparative Example 2

In this comparative example a device was made having a prior artstructure, as shown in FIG. 1.

The device was made according to the General Procedure with thefollowing configuration:

Substrate: glass

Anode: ITO

Hole transport layer: CBP (302 Å)

-   Emitter: G1 (405 Å)

Electron transport layer: DPA (103 Å)

Electron transport layer: AlQ(303 Å)

Cathode: LiF(10 Å)/Al(505 Å)

The device emits green light with an electroluminescent efficiency of 15cd/A at 7 V, and a radiance of 25,000 cd/m² at 12 V. Its radiance vs.voltage curve is shown in FIG. 5, as 5-b. Its efficiency vs. voltagecurve is shown in FIG. 6, as 6-b.

Compared to devices made with MPMP as the hole transport layer, the CBPbased devices show higher radiance and lower threshold voltage forinjection while the MPMP based devices show higher efficiency, as shownin FIGS. 5 and 6.

Comparative Example 3

In this comparative example a device was made having a prior artstructure, which has been disclosed in US 2003/0075720 A1, and is shownin FIG. 2. Layer 201 is the transparent substrate, over which anode 202is formed. Layer 203 is the hole transport layer; 205 the light emitterlayer, 206 and 207 are two electron transport layers and 208 is thecathode. A thin interface layer 204 is inserted between the holetransport layer and the light emiter layer to enhance the deviceluminance efficiency. The thickness of the interface layer is in therange of 0.1 to 5 nm. Typical materials used as the interface layer are:anthracene, terphenyl, quaterphenyl, hexaphenylbenzene, phenyloxazole,and spirobifluorene.

The device was made according to the General Procedure with thefollowing configuration:

Substrate: glass

Anode: ITO

Hole transport layer: MPMP (303 Å)

Thin interface layer: anthracene (4 Å)

Emitter: G1 (402 Å)

Electron transport layer: DPA (103 Å)

Electron transport layer: AlQ(301 Å)

Cathode: LiF(10 Å)/Al(505 Å)

The device emits green light with an electroluminescent efficiency of1.3 cd/A at 15 V, and a radiance of 800 cd/m² at 20 V. These numbers aremore than one order of magnitude lower than devices made with MPMP aloneas the hole transport layer as shown in Example 1. Clearly, the additionof a thin interface layer between the hole transport layer and theemitter layer did not improve the device properties.

Example 1

In this example a new device was made having the structure shown in FIG.3.

A series of devices were made according to the General Procedure withthe following device configuration:

Substrate: glass

Anode: ITO

New Charge Transport layer, a Spatially-doped hole transport layer:

CBP/MPMP/CBP Emitter layer: G1

Electron transport layer: DPA

Electron transport layer: AlQ

Cathode: LiF/Al

The thickness of thin MPMP guest sublayer is a substantially continuoussublayer (and not islands of guest material) and varies in thinknessfrom 50 Å to 10 Å. The weight % of guest material in the hole transportlayer was 13.31% wt; 5.35% wt; 4.60%; and 2.73%, for Example 1a,1b,1c,and 1d, respectively. The device configurations, peak efficiency, andpeak radiance of devices are summarized in Table I, which illustratesthat the new charge transport layer, in this example the spatially-dopedMPMP sublayer in the host CBP hole transport material improved thedevice performance dramatically compared to devices using MPMP or CBPalone as the hole transport layer or using MPMP with an anthraceneinterlayer.

The radiance vs voltage and efficiency vs voltage curves of a devicemade with a 10 Å thick MPMP layer spatially doped in CBP is shown inFIG. 5 as 5-a, and FIG. 6 as 6-a, in comparison with devices made witheither MPMP or CBP alone. Device made with 10 Å spatially doped MPMPlayer shows both high efficiency and high radiance, combining thepositive attributes of both MPMP and CBP. TABLE I Device configurations,peak efficiency, and peak radiance of devices made with spatially dopedhole transport layer. Device Peak efficiency, Peak radiance, Examplesconfiguration cd/A cd/m2 Example 1-a CBP(204 Å) 21 cd/A at 9 V 27,000cd/m2 at 14 V MPMP(53 Å) CBP(202 Å) G1(402 Å) DPA(101 Å) AlQ(301 Å)LiF(10 Å) Al(505 Å) Example 1-b CBP(207 Å) 24 cd/A at 14 V 34,000 cd/m2at 18 V MPMP(22 Å) CBP(204 Å) G1(405 Å) DPA(101 Å) AlQ(303 Å) LiF(10 Å)Al(504 Å) Example 1-c CBP(204 Å) 22 cd/A at 7 V 50,000 cd/m2 at 13 VMPMP(15 Å) CBP(202 Å) G1(404 Å) DPA(102 Å) AlQ(303 Å) LiF(10 Å) Al(503Å) Example 1-d CBP(201 Å) 24 cd/A at 7 V 60,000 cd/m2 at 18 V MPMP(11 Å)CBP(202 Å) G1(401 Å) DPA(102 Å) AlQ(301 Å) LiF(10 Å) Al(505 Å)

1. A charge transport layer comprising a host charge transport materialand a guest charge transport material, wherein said guest material isspatially-doped within the host material.
 2. A charge transport layeraccording to claim 1, wherein the host material is a hole transportmaterial and the guest material is a hole transport material.
 3. Acharge transport layer according to claim 2, wherein the lowestunoccupied molecular orbital level of the guest hole transport materialis higher than the lowest unoccupied molecular orbital level of the hosthole transport material.
 4. A charge transport layer according to claim2, wherein the host material is different from the guest material, andeach of the host material and guest material is selected fromN,N′-diphenyl-N,N′-bis(3-methylphenyl)-[1,1′-biphenyl]4,4′-diamine(TPD), 1,1-bis[(di4-tolylamino) phenyl]cyclohexane (TAPC),N,N′-bis(4-methylphenyl)-N,N′-bis(4-ethylphenyl)-[1,1′-(3,3′-dimethyl)biphenyl]-4,4′-diamine(ETPD), tetrakis-(3-methylphenyl)-N,N,N′, N′-2,5-phenylenediamine (PDA),a-phenyl-4-N,N-diphenylaminostyrene (TPS), p-(diethylamino)benzaldehydediphenylhydrazone (DEH), triphenylamine (TPA),bis[4-(N,N-diethylamino)-2-methylphenyl](4-methylphenyl)methane (MPMP),1-phenyl-3-[p-(diethylamino)styryl]-5-[p-(diethylamino)phenyl]pyrazoline (PPR or DEASP), 1,2-trans-bis(9H-carbazol-9-yl)cyclobutane(DCZB),N-(1-naphthyl)-N-phenylamino]biphenyl (NPB or NPD), carbazolebiphenyl (CBP), porphyrinic compounds, polyvinylcarbazole,(phenylmethyl)polysilane, polythiophenes, polypyrroles, polyanilines andmixtures thereof.
 5. A charge transport layer according to claim 2,wherein the host material comprises a compound having at least twocarbazole groups and the guest material comprises a triarylmethanecompound.
 6. A charge transport layer according to claim 2, wherein thehost material comprises Formula I below:

wherein E is selected from a single bond, (CR¹R²)_(m), O, S,(SiR¹R²)_(m) wherein m is an integer of 1 to 20, wherein R¹ and R² areeach independently selected from H, F, alkyl, aryl, alkoxy, aryloxy,fluoroalkyl, fluoroaryl, fluoroalkoxy, and fluoroaryloxy, and wherein R¹and R² can, when taken together, can form 5- or 6-membered rings; andwherein the guest hole transport material comprises Formula II below:

wherein: Ar¹ can be the same or different at each occurrence and isselected from aryl and heteroaryl; R³ can be the same or different ateach occurrence and is selected from H, alkyl, heteroalkyl, aryl,heteroaryl, arylalkylene, heteroarylalkylene, C_(n)H_(a)F_(b), andC₆H_(c)F_(d); or adjacent R³ groups can be joined to form 5- or6-membered rings; X can be the same or different at each occurrence andis selected from R³, alkenyl, alkynyl, N(R¹)₂, OR¹, OC_(n)H_(a)F_(b),OC₆H_(c)F_(d), halide, NO₂, OH, CN, and COOR¹; n is an integer, and a,b, c, and d are 0 or an integer such that a+b=2n+1, and c+d =5.
 7. Acharge transport layer according to claim 2, wherein the host is CBP andthe guest is MPMP.
 8. A charge transport layer according to claim 1,wherein the host material is an electron transport material and theguest material is an electron transport material.
 9. A charge transportlayer according to claim 8, wherein the highest occupied molecularorbital level of the guest electron transport material is lower than thehighest occupied molecular orbital level of the host electron transportmaterial.
 10. A charge transport layer according to claim 8, wherein thehost material is different from the guest material, and each of the hostmaterial and guest material is selected from metal chelated oxinoidcompounds, azole compounds, quinoxaline derivatives, phenanthrolinederivatives, and mixtures thereof.
 11. A charge transport layeraccording to claim 1, wherein the host material is at least 60% byweight of the charge transport layer.
 12. A charge transport layeraccording to claim 1, wherein the host material is at least 75% byweight of the charge transport layer.
 13. A charge transport layeraccording to claim 1, wherein the charge transport layer has a firstthickness and the guest material comprises a thin film having a secondthickness within the host material, and the second thickness is lessthan 50% of the first thickness.
 14. A charge transport layer accordingto claim 13, wherein the second thickness is from 1% to 20% of the firstthickness.
 15. An organic electronic device comprising a chargetransport layer comprising a host charge transport material and a guestcharge transport material, wherein said guest material is spatiallydoped within the host material.
 16. A device according to claim 15,wherein the host material is a hole transport material and the guestmaterial is a hole transport material.
 17. A device according to claim16, wherein the host material comprises a compound having at least twocarbazole groups and the guest material comprises a triarylmethanecompound.
 18. A charge transport layer according to claim 16, whereinthe host material comprises Formula I below:

wherein E is selected from a single bond, (CR¹R²)_(m), O, S,(SiR¹R²)_(m) wherein m is an integer of 1 to 20, wherein R¹ and R² areeach independently selected from H, F, alkyl, aryl, alkoxy, aryloxy,fluoroalkyl, fluoroaryl, fluoroalkoxy, and fluoroaryloxy, and wherein R¹and R² can, when taken together, can form 5- or 6-membered rings; andwherein the guest hole transport material comprises Formula II below:

wherein: Ar¹ can be the same or different at each occurrence and isselected from aryl and heteroaryl; R³ can be the same or different ateach occurrence and is selected from H, alkyl, heteroalkyl, aryl,heteroaryl, arylalkylene, heteroarylalkylene, C_(n)H_(a)F_(b), andC₆H_(c)F_(d); or adjacent R³ groups can be joined to form 5- or6-membered rings; X can be the same or different at each occurrence andis selected from R³, alkenyl, alkynyl, N(R¹)₂, OR¹, OC_(n)H_(a)F_(b),OC₆H_(c)F_(d), halide, NO₂, OH, CN, and COOR¹; n is an integer, and a,b, c, and d are 0 or an integer such that a+b=2n+1, and c+d =5.
 19. Adevice according to claim 15, wherein the host material is an electrontransport material and the guest material is an electron transportmaterial.
 20. A device according to claim 15, wherein the device isselected from a light-emitting diode, a light-emitting diode display, alaser diode, a photodetector, photoconductive cell, photoresistor,photoswitch, phototransistor, phototube, IR-detector, photovoltaicdevice, solar cell, light sensor, photoconductor, electrophotographicdevice, transistor, or diode.
 21. A device according to claim 19,wherein the highest occupied molecular orbital level of the guestelectron transport material is lower than the highest occupied molecularorbital level of the host electron transport material.
 22. A deviceaccording to claim 16, wherein the lowest unoccupied molecular orbitallevel of the guest hole transport material is higher than the lowestunoccupied molecular orbital level of the host hole transport material.